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NROB60H3 (157)
Chapter 6

Chapter 6 Notes

10 Pages
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Department
Neuroscience
Course Code
NROB60H3
Professor
Janelle Leboutillier

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Chapter 6 Notes
-In addition to the molecule itself, a neurotransmitter system includes all the molecular machinery
responsible for transmitter synthesis, vesicular packaging, reuptake and degradation, and
transmitter action
-Dale termed the neurons that use the acetylcholine transmitter = cholinergic
-Noradrenergic: Neurons that use the amine neurotransmitter norepinephrine (NE)
Elements of Neurotransmitter Systems
-Presynaptic axon terminal
oNeurotransmitter-synthesizing enzymes
oSynaptic vesicle transporters
oReuptake transporters
oDegradative enzymes
-Postsynaptic Dendrite
oTransmitter-gated ion channels
oG-protein-coupled receptors
oG-proteins
oG-protein-gated ion channels
oSecond messenger cascades
Criteria For A Molecule To Be Considered A Neurotransmitter:
1) The molecule must be synthesized and stored in the presynaptic terminal
2) The molecule must be released by the presynaptic axon terminal upon stimulation
3) The molecule, when experimentally applied, must produce a response in the postsynaptic cell that
mimics the response produced by the release of neurotransmitter from the presynaptic neuron
Localization of Transmitters and Transmitter-Synthesizing Enzymes
-First step: Show that the molecule is localized in and synthesized by particular neurons
oTwo techniques in studying this:
Immunochemistry Method for viewing location of specific
molecules/proteins in sections of brain tissues
In Situ Hybridization Method for localizing specific mRNA transcripts for
proteins
Immunochemistry: Used to anatomically localize particular molecules to particular cells
-Once NT has been chemically purified, it is injected into the bloodstream of animal, where it
stimulates an immune response
-Immune response Generates large proteins called antibodies
-Antibodies can bind tightly to specific sites on the foreign molecule (e.g. the transmitter candidate)
-Best antibodies bind very tightly to the transmitter of interest
-Antibody molecules can be recovered from a blood sample of the immunized animal and
chemically tagged with a colourful marker and applied to sections of brain tissue
-Antibodies label only those cells that contain NT candidate
-Immunochemistry can be used to localized any molecule for which a specific antibody can be
generated, including the synthesizing enzymes for transmitter candidates
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In Situ Hybridization: Useful for confirming that a cell synthesizes a particular protein or peptide
-There is a unique mRNA molecule for every polypeptide synthesized by a neuron
-mRNA transcript consists of four different nucleic acids linked together in sequence to form strand
-If sequence of strand is known it is possible to construct in the lab a complementary strand that
will stick, to the mRNA molecule
oComplementary strand = Probe
-Process by which probe bonds to mRNA molecule = Hybridization
-In order to see if mRNA for particular peptide is localized in a neuron, probe is chemically labeled
(by radioactive) and applied to a section of brain tissue that is sensitive to radioactive emissions
oProbe sticks to complementary mRNA strands, and extra probes are washed away
oLook for neuron containing label
oFilm is developed like a photograph, and negative images of radioactive cells are visible
as clusters of small dots
Autoradiography
Studying Transmitter Release
-Specific set of cells of axons can be stimulated while taking samples of fluids bathing their
synaptic targets
-Biological activity of the sample can then be tested to see if it mimics the effect of the intact
synapses
-Sample can be chemically analyzed to reveal the structure of the active molecule
Studying Synaptic Mimicry
-Molecule must evoke the same response as that produced by the released of naturally occurring
neurotransmitter from the presynaptic neuron
-Method used: Micrionophoresis
oEnables a researcher to apply drugs or neurotransmitter candidates in very small amounts
to the surface of neurons. The responses generated by the drug can be compared to those
generated by synaptic stimulation
oMicroelectrode in the postsynaptic neuron can be used to measure the effects of the
transmitter candidate on the membrane potential
oIf ionophoretic application of the molecule causes electrophysiological changes that
mimic the effects of transmitter released at the synapse, and if the other criteria of
localization, syntheisis and release have been met, then the molecule and the transmitter
are considered to be the same chemical
Studying Receptors
-No two NT bind to the same receptors, but one NT can bind to many different receptors
-Receptor Subtype: Each of the different receptors a NT binds to
oE.g. ACh acts on two different subtypes
Approaches to Studying Receptor Subtypes:
1) Neuropharmacological Analysis (of synaptic transmission)
2) Ligand Binding Methods
3) Molecular Analysis of Receptor Proteins
Neuropharmacological Analysis
www.notesolution.com
-Skeletal muscle and heart muscle respond differently to various cholinergic drugs
oNicotine is a receptor agonist in skeletal muscle but no effect in heart
oMuscarine has little or no effect on skeletal muscle but is an agonist at the cholinergic
receptor subtype in the heart
-Two ACh receptors can be distinguished by the actions of different drugs
-Two ACh receptors can also be distinguished by selective antagonists
oCurare inhibits action of ACh at nicotinic receptors
oAtropine inhibits action of ACh at muscarinic receptors
-Different drugs were used to distinguish several subtypes of glutamate receptors
oAMPA receptors
oNMDA receptors
oKainate receptors
Glutamate activates all three receptors but AMPA only acts at AMPA Rs, etc.
-NE receptors are split into two types:
oGABAa and GABAb
Ligand-Binding Methods
Opiates: A broad class of drugs that are both medically important and commonly abused
-Effects: Pain relief, euphoria, depressed breathing, constipation
-Any chemical compound that binds to a specific site on a receptor = Ligand for that receptor
oLigand can be agonist, antagonist, or chemical NT itself
oLigand-binding methods have been enormously important for mapping the anatomical
distribution of different neurotransmitter receptors in the brain
Molecular Analysis
-Two types of NT receptor proteins:
oTransmitter-gated ion channels
oG-Protein-coupled (metabotropic) receptors
-Many polypeptides serve as subunits of functional receptors, and subunits are composed of several
polypeptides
oE.g. GABA receptors contain 5 subunits
The Neuropharmacology of Some Receptor Subtypes
Neurotransmitter Receptor SubtypeAgonist (Mimics NT)Antagonist (Blocks
NT)
Acetylcholine (ACh) Nicotinic Receptor
Muscarinic Receptor
Nicotine
Muscarine
Curare
Atropine
Norepinephrine (NE)α Receptor
β Receptor
Phenylephrine
Isoproterenol
Phenoxybenzamine
Propranolol
Glutamate (Glu) AMPA
NMDA
AMPA
NMDA
CNQX
AP5
GABA GABAa
GABAb
Muscimol
Baclofen
Bicuculline
Phaclofen
ATP P2x
A type
ATP
Adenosine
Suramin
Caffeine
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Description
Chapter 6 Notes - In addition to the molecule itself, a neurotransmitter system includes all the molecular machinery responsible for transmitter synthesis, vesicular packaging, reuptake and degradation, and transmitter action - Dale termed the neurons that use the acetylcholine transmitter = cholinergic - Noradrenergic: Neurons that use the amine neurotransmitter norepinephrine (NE) Elements of Neurotransmitter Systems - Presynaptic axon terminal o Neurotransmitter-synthesizing enzymes o Synaptic vesicle transporters o Reuptake transporters o Degradative enzymes - Postsynaptic Dendrite o Transmitter-gated ion channels o G-protein-coupled receptors o G-proteins o G-protein-gated ion channels o Second messenger cascades Criteria For A Molecule To Be Considered A Neurotransmitter: 1) The molecule must be synthesized and stored in the presynaptic terminal 2) The molecule must be released by the presynaptic axon terminal upon stimulation 3) The molecule, when experimentally applied, must produce a response in the postsynaptic cell that mimics the response produced by the release of neurotransmitter from the presynaptic neuron Localization of Transmitters and Transmitter-Synthesizing Enzymes - First step: Show that the molecule is localized in and synthesized by particular neurons o Two techniques in studying this: Immunochemistry Method for viewing location of specific moleculesproteins in sections of brain tissues In Situ Hybridization Method for localizing specific mRNA transcripts for proteins Immunochemistry: Used to anatomically localize particular molecules to particular cells - Once NT has been chemically purified, it is injected into the bloodstream of animal, where it stimulates an immune response - Immune response Generates large proteins called antibodies - Antibodies can bind tightly to specific sites on the foreign molecule (e.g. the transmitter candidate) - Best antibodies bind very tightly to the transmitter of interest - Antibody molecules can be recovered from a blood sample of the immunized animal and chemically tagged with a colourful marker and applied to sections of brain tissue - Antibodies label only those cells that contain NT candidate - Immunochemistry can be used to localized any molecule for which a specific antibody can be generated, including the synthesizing enzymes for transmitter candidates www.notesolution.com
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